A video RAM (VRAM), sometimes called dual-port RAM, is a DRAM (dynamic random access memory) with a serial access memory. The serial access memory permits a block of stored data to be rapidly accessed, while the normal access function of the DRAM is also occurring. The information in the serial access memory is normally obtained from, or input into, a primary memory on the VRAM. The primary memory is configured as a DRAM and is accessed according to DRAM protocols.
Information may be put into the VRAM at DRAM address speeds and output through the serial access port, or vice-versa. This is convenient for video applications because some address sequences, such as pixels in a raster scan, are predetermined.
The VRAM permits both serial access memory input and serial access memory retrieval of the access memory, but not simultaneously. Therefore, if both input and retrieval are to be accomplished, a logic protocol must be established. It would be desirable to permit simultaneous storage to and retrieval from a memory while also permitting random access to a main memory.